The present invention is directed to dishwashing appliances, and particularly dishwashers which include upper and lower dish racks and separate spray arms associated with each rack. U.S. Pat. No. 3,180,348, which issued to J. F. Clearman on Apr. 27, 1965 and U.S. Pat. No. 3,854,762, which issued to Ray W. Spiegel et al on Dec. 17, 1974, both of which are assigned to the assignee of the present invention, describe dishwashing appliances which contain dual spray arms, the upper of which is driven by a liquid jet or stream produced by a recirculation pump.
Both of the above patents disclose a dishwasher which contains upper and lower dish racks which may be withdrawn to permit loading. Mounted beneath the lower dish rack is a spray arm which rotates to direct washing liquid, which may be water or water with cleansing agents added, to articles loaded in the lower rack and includes a central aperture through which a jet of liquid is directed toward the upper dish rack.
A rotatable upper spray arm mounted to the upper dish rack receives the jet of washing liquid in a conical receiver which directs the liquid to the upper spray arm. Nozzles spaced along the spray arms are positioned to cause the spray arm assembly to rotate and distribute washing liquid over the dishes.
In order to be efficient, the upper spray arm receiver must be centrally located with respect to the jet of washing liquid produced by the recirculation pump. Misalignment produces unbalanced forces on the upper spray arm and inefficient distribution of washing liquid. Alignment of the upper spray arm and liquid jet has proven difficult to accomplish in the past since it is necessary that the upper dish rack be movable with respect to the dishwasher in order to permit dishes to be conveniently loaded. The above mentioned U.S. Pat. No. 3,180,348 discloses a mechanism for manually adjusting the horizontal position of the upper spray arm with respect to the upper dish rack by manual rotation of an eccentric bearing mounting. It thus has been necessary to provide means which will accurately position the upper rack with respect to the cabinet and also accurately position the upper spray arm with respect to the upper rack. Close tolerance manufacturing and assembly techniques have been necessary to provide the required positional accuracy.
These methods materially increase the manufacturing expenses involved and in addition, have not always proven successful. Factors such as remaining production tolerances, the necessary adjustability of the top rack, distortion of a lower dish rack mounted jet stream directing tower and the position of the lower arm with respect to the cabinet all may still contribute to produce misalignment of the upper spray arm with respect to the jet of washing liquid.